The invention relates to a method for monitoring an operating status of an anode furnace, wherein the anode furnace is formed from a plurality of heating ducts and furnace chambers, wherein the furnace chambers serve for receiving anodes and the heating ducts serve for controlling the temperature of the furnace chambers, wherein the anode furnace comprises at least one furnace unit having a heating zone, a firing zone and a cooling zone, wherein a suction device is arranged in the heating zone and a burner device is arranged in the firing zone, wherein, by means of the burner device, combustion air is heated up in the heating ducts of the firing zone, and wherein, by means of the suction device, hot air is sucked out of the heating ducts of the heating zone.
The present method is applied in the production of anodes that are required for fused-salt electrolysis for the production of primary aluminum. These anodes are produced in a molding procedure as so-called “green anodes” or “raw anodes”, from petroleum coke, to which pitch is added as a binding agent, the anodes being sintered in an anode furnace subsequently to the molding procedure. This sintering process is realized in a heat treatment process which takes place in a defined manner, and during which the anodes pass through three phases, namely a heating phase, a sintering phase and a cooling-down phase. In this case, the raw anodes are situated in a heating zone of a “fire” that is composed of the heating zone, a firing zone and a cooling zone and that is formed in the anode furnace, the raw anodes being pre-heated by the waste heat of already fully sintered anodes that originates from the firing zone, prior to the pre-heated anodes being heated to the sintering temperature of approximately 1200° C. in the firing zone. According to the state of the art as it is known, for example, from the document EP 1 785 685 A1, the different above-described zones are defined by an alternately continuous arrangement of different modules above furnace chambers or heating ducts that receive the anodes.
The firing zone, which is arranged between the heating zone and the cooling zone, is defined by positioning a burner device above selected furnace chambers or heating ducts. Anodes that have been burned directly prior thereto, which means that have been heated to the sintering temperature, are situated in the cooling zone. Above the cooling zone, a blower device is arranged, by means of which air is blown into the heating ducts of the cooling zone. By means of a suction device that is arranged above the heating zone, the air is guided, via the heating ducts, from the cooling zone through the firing zone into the heating zone, and, from the latter, in the form of flue gas, guided through a flue gas cleaning system, being released into the surroundings. The suction device and the burner device form a furnace unit together with the blower device and the heating ducts.
The above-described modules are shifted at regular time intervals along the heating ducts in the direction of the raw anodes that are arranged in the anode furnace. In this way, there can be provision for an anode furnace comprising several furnace units, the modules of which are shifted, subsequently to one another, above the furnace chambers or heating ducts for subsequent heat treatment of the raw anodes or anodes. In case of such anode furnaces, which can be embodied as open anode furnaces or annular anode furnaces in different designs, there is the problem that a volumetric flow of the air, which is channeled through the anode furnace, can only be measured with an unjustifiably high complexity. Determining the volumetric flow is in particular required for regularly monitoring an operating status of an anode furnace. In this way, it is to be ensured that sufficient oxygen for combusting a combustible material of the burner device is available in the heating ducts of the anode furnace. Since, due to the meander-shaped rectangular geometry of the heating ducts, a direct volumetric flow measurement is not possible, an attempt is made to determine the volumetric flow by an indirect measurement, for example a pressure measurement. Such an estimation of the volumetric flow, however, often leads to useless results if, for example, a heating duct covering is open or improperly closed, or if a heating duct is clogged or blocked. Measuring the volumetric flow by means of a venturi tube also leads to unsatisfactory results since the differential pressures needed for measuring cannot be produced. In practice, a volumetric flow evaluation is therefore performed at regular time intervals by qualified furnace personnel in the course of furnace inspections. If a functional disorder of the anode furnace is detected, the same is manually switched off by the furnace personnel in this case. This can, however, lead to dangerous operating statuses of the anode furnace, which can lead to deflagrations, fires or explosions, possibly not being detected early enough.